Accelerometer



June 9, 1953 J. J. GILVARRY ET AL ACCELEROMETER Filed March 5, 1949 2 52 3 l 24 LOCAL o/v- OFF ON- OFF PULSE 7'RI66ER TRIGGER OSC/LLATORCIRCUIT CIRCUIT t I i 26 DIGITAL ACCELERATION COMPUTER .m. GILVAR RY or.RUTLAND IN VEN TORS ATTORNEY i atentecl June 9, 1951? ACCELERQMETER JohnJ. Gilvarry, Santa Monica, and David F. Rutland, Pacific Palisades,Califl, assignors to North American Aviation, Inc.

Application March 5, 1949, Serial No. 79,768

5 Claims.

This invention relates to the measurement of acceleration andparticularly to the measurement of the acceleration of a body in spaceby the variation in relative velocity of accelerated and unacceleratedmasses in space.

An object of this invention is to provide a method and means for themeasurement of acceleration which is virtually independent of frictionand hysteresis, has no associated natural frequency, and which iscapable of measuring a wide range of accelerations with precision.

It is a further object of the invention to provide an accelerationmeasuring device which yields an output signal in digital form.

A further object of this invention is to provide a means for measuringaccelerations dependent on the apparent change in velocity of objects infree flight within an enclosure subject to accelerations.

Other objects of invention will be apparent from the followingdescription taken in conjunction with the accompanying drawing in whichFig. 1 is a partial schematic view of the device; and

Fig. 2 is a schematic view of the arrangement shown in Fig. 1.

In Fig. 1 is shown an evacuable container I mounted on a base 2.Container I carries light sources 3, 4, and 5, mounted on one sidethereof with apertures for admitting light into the con tainer I.oppositely mounted on container I are light detecting means I, 8, and 9,such as photocells, capable of detecting light in container I throughsmall apertures 6 in container I. Mounted on the longitudinal axis ofcontainer I is projectile emitter l9 operatively positioned to emitparticles of matter'along the longitudinal axis of the container.Projectile emitter I is a compressed air gun, spring gun, water spraynozzle, or any other similar device capable of ejecting uniformparticles at a substantially uniform velocity. Operatively associatedwith light detecting means I, 8, and 9 is an electronic timing means II.

In using this device to measure accelerations of container I andassociated apparatus, particles of matter are emitted chronologicallyalong the longitudinal axis of the container. As each particle crosses atransverse plane formed by light source and light detecting means 1, itinterrupts the beam of light received by light detecting means I fromlight source 5. This interruption causes the generation of an electricalsignal which is fed to electronic timer I I. When the emitted particlereaches positions in the container opposite light detectin means 8 and9, similar signals are generated in a like manner. Thus an accuratemeans is provided for detecting the presence of the particles at threedifferent points in their path through the container. Furthermore, sinceeach of the light detecting means sends a signal to electronic timer IIwhenever a particle passes it, the electronic timer can be arranged toread both the time of transit of particles over each segment of itspath, and the difference between the transit times over each of the twosegments of the path.

When the device is at rest or moving through space with a uniformvelocity, the time elapsed between the signals successively generated bydetecting means I, 8, and 9, are equal. However, if the device is givenan acceleration along the longitudinal axis of container I, the timeelapsed between the successive signals from the detecting means is nolonger equal. This phenomenon is due to the fact that the particleswhich are in free flight experience no acceleration. Hence, theirapparent time of flight through the accelerated container is eitherlonger or shorter than the time observed when the container is notaccelerated depending on the direction of acceleration. It has beenestablished theoretically that a definite mathematical relationshipexists between the acceleration applied and the time elapsed between thesuccessive signals. Or, in other words, the measured'elapsed times arean indirect measure of the acceleration applied to the device. The exactrelationship is given by the formula where A is the accelerationmeasured, Z1 is the distance between the first and second slit, Z2 isthe distance between the second and third slit, h is the time requiredfor a particle to traverse the distance between the first and secondslits and is is the time required for the same particle to traverse thedistance between the second and last slits. Figure 2 shows in detail howthe acceleration of container l is obtained by use of information gainedby detecting means I, 8, and 9. Projectile emitter I0 is shown in detailin Fig. 2 as a spring operated gun, although it is to be understood anyother suitable means such as a compressed air gun could be used. In Fig.2 accurately machined steel balls (one millimeter in diameter as anexample) are dropped consecutively one at a time from hopper II intobarrel l8 by action of shutter 19 and plunger 20 coordinated by cam 2|.Spring 22, being loaded by cam-actuated movement of plunger 20 propelsthe balls one by one across container I. As each ball interrupts thelight received by detectors 1, 8, and 9, a signal is generated which isfed to On-OiT trigger circuits (shown and described in detail involume19 of' the Massachusetts Institute of Technology Radiation LaboratorySeries entitled Waveforms, by Chance, Hughes, Mac- Nichol, Sayre, andWilliams, sec. 5.12, page r837 et seq.) 23 and 24 the function ofwhichiis-to connect the output of high frequency local oscillator 25 todigital computer 21': for a length of time equal to I51 and for a?length; of: time equal. to it. Digital computer 26 then uses these qu'antities to compute the aforesaid equation yielding, the acceleration ofcontainer I in digital form. A preeminent advantage gained by this:device: is\ that the acceleration measured is presented in digital formwhich facilitates, dealing wit-h the information by means of digitalcomputers.

After the balls have. completed; their flight through container I theyare lodged incylindrical. catcher 21 rotatedby' motor 28-. at suchvelocity as to. cause-the. spient balls' to cling to the surface of,-catcher 2:'|;- by centrifugal force;

Instead of steel@balls,-. of course it. is possible to use many; othertypes ofparticles, notably oil droplets of uniformsize, by appropriatemodification: of projectile emitter l0.

Althoughthe invention hasbeen describedand illustrated in detail, it isto be clearly understood that the sameisby way of illustration andexample only and is not. to be' taken by were of limitation, the spiritand scope of this invention being limited only: by termsrof the.-appended claims.

We-claim:

1. Measuringmeans.comprising-.acontainen sub ject to acceleration,,means. for projecting; a. p111:- ralityof. small masses. uniformly intosaid container ina: predetermined; directiom, means" for instantaneouslysensing the; presence.- of said masses at predetermined planea in: thecontainer, and means operably' associated with; said sensing means formeasuring the'time necessaryfon each of said. masses to travel frorm oneof. saidipredetermined planesv to. another,- tottherebyobtain quantitiesof which the; acceleratiom to: which said container is subject: in.-said predetermined direction a: function..

2. A measuring: device: comprising; a: container subjecttoaccelerations, means= for projecting into said container a pluralityof small! masses with a substantially uniform velocity along a pathparallel to the direction inlwhich said container is generally subjectto acceleration, means for measuring the time necessary for said massesto traverse predetermined distances in said container to measure therebya quantity of which the accelerations to which said container issubjected are a function.

3. A device as recited in claim 2 in which said meanafor measuring timecomprises a plurality of light sources and light d'etectin'g meanspositioned in complement at predetermined intervals adjacent to saidpath of said masses, means responsive to said light-detecting means fordetermining the time for passage of the shadow cfi said masses: oversaid predetermined intervals, anmmeans for comparing said determinedtime for each' ofsaid' predetermined intervals to thereby.obtaimameasure of the acceleration to which said container is subjected.

4 A- device as recited in claim 2 in which said means for measuring timecomprises a plurality of sensing. elements which: are sensitive to. thevery near presence. of said. mas'sesu predeterminately spaced alongsaidpath off said masses, and means responsive: to" said: sensing elementsfor electronically determining. the time of! passage ofsaid'massesover'said'predetermined spaces. to. thereby obtain ameasureof the: amce-leratiorr. to which said. container is subject.

5.. Measuring: means comprising a container subject. to accelerations;a. plurality of small masses; meansfor. projecting said: masses in: saidcontainer inxat. least one; predetermined direction; meansfoninstantaneously sensing the presence of said: masses at predetermined)-points; in saidcontainen. and: means. operably' associated with said:sensing; means for: measuring the: time necessary for: each of said:masses: to: travels the distance between saidl predetermined; points insaid container, to thereby measure a quantity of which the:accelerations to which. said. container is subiecc' are; function;

JOHN J. GILVARsR'i-SRI DAVIDELRU'ILANDE.

Referenced Gited in the: of: thin patent UNITED STATES PATEN Fs' NumberName Date 2,2'943301 Eggers Sept. 1,.1942 2,319,932 J'acobs May 25,2,355,128 Whitl'ock 1 Aug. 81,. 1544 23574620. Abraham c Dec. 28; 1548EQREIGNJ Number Country Date seer-32' France Apr. 27; 1922

